In the mobile communications industry, utilization of a repeater or relay has been regarded as one possible solution to efficiently extend the coverage of a base station of the network. One problem involved in using repeater, however, is the noise enhancement in the uplink, which can decrease the uplink capacity of the communication system. In multiple-input, multiple-output (MIMO) systems in which one repeater may have multiple antennas, the noise enhancement problem may be much more serious than in typical single-input, single-output (SISO) systems. For example, if there are M number of SISO repeaters connected to a base station, the noise enhancement in the uplink is proportional to the number M. If there are M number of MIMO repeaters having N number of antenna elements each connected to the base station, the noise enhancement in the uplink is proportional to the product M×N, which quickly reach an unacceptable level. As the order of MIMO increases, for example, in which M×N is about 20×4, the noise enhancement in the uplink of the MIMO communications network raised by the utilization of MIMO repeaters will become increasingly significant. This is especially true as MIMO is deployed in wireless wide area networks (WWANs), such as cellular communication networks or in Wireless Interoperability fir Microwave Access (WiMAX) type networks in addition to wireless local area networks (WLANs) and/or personal area networks (PANs).
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